Responses of macrophage-associated antigen-expressing cells in the dental pulp of rat molars to experimental tooth replantation

Bacterial infection of the dental pulp is a major hindrance to successful pulp regeneration after tooth replantation. This study examined how macrophages and class II molecule-expressing cells of the pulp respond to tooth replantation, on the hypothesis that they contribute to the defence and repair of the traumatized pulp. Upper right first molars of 5-week-old male Wistar rats were replanted immediately after extraction; contralateral untreated teeth served as controls. Pulpal cells expressing macrophage-associated antigens were immunohistochemically demonstrated at 0 h (immediately after the replantation) to 84 days postoperatively using antirat monoclonal antibodies OX6 (anti-class II molecules), ED1 (pan-macrophage antibody, reactive also with dendritic cells) and ED2 (anti-resident macrophages). Between 3 and 7 days postoperatively, ED1+ and OX6+ cells, but not ED2+ cells, were concentrated in areas of degeneration formed in the coronal pulp, and frequently showed a marked accumulation along the pulp–dentine border of the cuspal area. Confocal laser scanning microscopy revealed that some of the OX6+ cells with a dendritic profile extended several cytoplasmic processes into the dentinal tubules communicating with the enamel-free area at the tip of the cusp. From 14–84 days, approx. two-thirds of specimens exhibited pulp-tissue regeneration with increasing formation of reparative dentine. Following the formation of sound reparative dentine, cells positive to each antibody were distributed more centrally in the pulp than in the controls, and thus did not show any accumulation along the pulp–dentine border. However, in the other specimens where a bone-like hard tissue had formed in the pulp chamber, many ED1+ and OX6+ cells were still concentrated in the remaining pulp tissue and showed a marked accumulation along the pulp–dentine border. Few ED2+ cells were observed in these specimens. These findings suggest that, following tooth replantation, exudative macrophages are actively engaged in eliminating dentinal tubule-derived infectious stimuli and that class II molecule-expressing cells, most probably containing dendritic cells, are positioned strategically at the outermost portion of the injured pulp to monitor incoming antigens. The intensity of the pulpal defence reaction may be dependent on the status of hard-tissue formation, which influences the amount of incoming antigens.